Hi,
If you want a good AD Domain Controller (and not only that!), Try NethServer.
It's based on CentOS, but you'll have a very friendly and powerful community forum to help you.
I still use Zentyal as an e-mail server because I can use it as a multi domain email server and also as an authoritative DNS because of the graphical interface, even I have some issues with reverse zones.
Kind regards,
Gabriel